In a manufacturing pipeline, there is a point where the time spent at a
given station is based on the mix of product types present at that station.
The metric involved is viscosity, and the time spent at that station can be
calculated as a function of average viscosity of all products at the
station.

What I want to do is schedule several products to flow through the pipeline,
and calculate their time to completion. Most of the scheduling applications
I have seen require independent times for each product, or independent
stochastic approximations.

Has anyone seen or used formulas/functions that allow interaction? Maybe
different sizes, weights, or combined pressures through a pipe?